Endovascular electrolytically detachable wire and tip for the formation of thrombus in arteries, veins, aneurysms, vascular malformations and arteriovenous fistulas

ABSTRACT

An artery, vein, aneurysm, vascular malformation or arterial fistula is occluded through endovascular occlusion by the endovascular insertion of a platinum wire and/or tip into the vascular cavity. The vascular cavity is packed with the tip to obstruct blood flow or access of blood in the cavity such that the blood clots in the cavity and an occlusion if formed. The tip may be elongate and flexible so that it packs the cavity by being folded upon itself a multiple number of times, or may pack the cavity by virtue of a filamentary or fuzzy structure of the tip. The tip is then separated from the wire mechanically or by electrolytic separation of the tip from the wire. The wire and the microcatheter are thereafter removed leaving the tip embedded in the thrombus formed within the vascular cavity. Movement of wire in the microcatheter is more easily tracked by providing a radioopaque proximal marker on the microcatheter and a corresponding indicator marker on the wire. Electrothrombosis is facilitate by placing the ground electrode on the distal end of the microcatheter and flowing current between the microcatheter electrode and the tip.

This application is a continuation of application Ser. No. 08/801,795filed Feb. 14, 1997, issued as U.S. Pat. No. 5,855,578, which in turnwas a continuation of application Ser. No. 08/485,821, filed Jun. 6,1995, now abandoned, and which in its turn was a continuation-in-partapplication of application Ser. No. 07/492,717, filed Mar. 13, 1990,issued as U.S. Pat. No. 5,122,136.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method and apparatus for endovascularelectrothrombic formation of thrombi in arteries, veins, aneurysms,vascular malformations and arteriovenous fistulas.

2. Description of the Prior Art

Approximately 25,000 intracranial aneurysms rupture every year in NorthAmerica. The primary purpose of treatment for ruptured intracranialaneurysm is to prevent rebleeding. At the present time, three generalmethods of treatment exist, namely an extravascular, endovascular andextra-endovascular approach.

The extravascular approach is comprised of surgery or microsurgery ofthe aneurysm or treatment site for the purpose of preserving the parentartery. This treatment is common with intracranial berry aneurysms. Themethodology comprises the step of clipping the neck of the aneurysm,performing a suture-ligation of the neck, or wrapping the entireaneurysm. Each of these surgical procedures is performed by intrusiveinvasion into the body and performed from outside the aneurysm or targetsite. General anesthesia, craniotomy, brain retraction and arachnoiddissection around the neck of the aneurysm and placement of a clip aretypically required in these surgical procedures. Surgical treatment ofvascular intracranial aneurysm can expect a mortality rate of 4-8% witha morbidity rate of 18-20%. Because of the mortality and morbidity rateexpected, the surgical procedure is often delayed while waiting for thebest surgical time with the result that an additional percentage ofpatients will die from the underlying disease or defect prior tosurgery. For this reason the prior art has sought alternative means oftreatment.

In the endovascular approach, the interior of the aneurysm is enteredthrough the use of a microcatheter. Recently developed microcatheters,such as those shown by Engelson, "Catheter Guidewire", U.S. Pat. No.4,884,579 and as described in Engelson, "Catheter for GuidewireTracking" U.S. Pat. No. 4,739,768 (1988), allow navigation into thecerebral arteries and entry into a cranial aneurysm.

In such procedures a balloon is typically attached to the end of themicrocatheter and it is possible to introduce the balloon into theaneurysm, inflate it, and detach it, leaving it to occlude the sac andneck with preservation of the parent artery. While endovascular balloonembolization of berry aneurysms is an attractive method in situationswhere an extravascular surgical approach is difficult, inflation of aballoon into the aneurysm carries some risk of aneurysm rupture due topossible over-distention of portions of the sac and due to the tractionproduced while detaching the balloon.

While remedial procedures exist for treating a ruptured aneurysm duringclassical extravascular surgery, no satisfactory methodology exists ifthe aneurysm breaks during an endovascular balloon embolization.

Furthermore, an ideal embolizing agent should adapt itself to theirregular shape of the internal walls of the aneurysm. On the contrary,in a balloon embolization the aneurysmal wall must conform to the shapeof the balloon. This may not lead to a satisfactory result and furtherincreases the risk of rupture.

Still further, balloon embolization is not always possible. If thediameter of the deflated balloon is too great to enter the intracerebralarteries, especially in the cases where there is a vasospasm,complications with ruptured intracranial aneurysms may occur. Theprocedure then must be deferred until the spasm is resolved and thisthen incurs a risk of rebleeding.

In the extra-intravascular approach, an aneurysm is surgically exposedor stereotaxically reached with a probe. The wall of the aneurysm isthen perforated from the outside and various techniques are used toocclude the interior in order to prevent it from rebleeding. These priorart techniques include electrothrombosis, isobutyl-cyanoacrylateembolization, hog-hair embolization and ferromagnetic thrombosis.

In the use of electrothrombosis for extra-intravascular treatment thetip of a positively charged electrode is inserted surgically into theinterior of the aneurysm An application of the positive charge attractswhite blood cells, red blood cells, platelets and fibrinogen which aretypically negatively charged at the normal pH of the blood. The thrombicmass is then formed in the aneurysm about the tip. Thereafter, the tipis removed. See Mullan, "Experiences with Surgical Thrombosis ofIntracranial Berry Aneurysms and Carotid Cavernous Fistulas", J.Neurosurg., Vol. 41, December 1974; Hosobuchi, "ElectrothrombosisCarotid-Cavernous Fistula", J. Neurosurg., Vol. 42, January 1975; Arakiet al., "Electrically Induced Thrombosis for the Treatment ofIntracranial Aneurysms and Angiomas", Excerpta Medica InternationalCongress Series, Amsterdam 1965, Vol. 110, 651-654; Sawyer et al.,"Bio-Electric Phenomena as an Etiological Factor in IntravascularThrombosis", Am. J. Physiol., Vol. 175, 103-107 (1953); J. Piton et al.,"Selective Vascular Thrombosis Induced by a Direct Electrical Current;Animal Experiments", J. Neuroradiology, Vol. 5, pages 139-152 (1978).However, each of these techniques involves some type of intrusiveprocedure to approach the aneurysm from the exterior of the body.

The prior art has also devised the use of a liquid adhesive,isobutylcyanoacrylate (IBCA) which polymerizes rapidly on contact withblood to form a firm mass. The liquid adhesive is injected into theaneurysm by puncturing the sac with a small needle. In order to avoidspillage into the parent artery during IBCA injection, blood flowthrough the parent artery must be momentarily reduced or interrupted.Alternatively, an inflated balloon may be placed in the artery at thelevel of the neck of the aneurysm for injection. In addition to therisks caused by temporary blockage of the parent artery, the risks ofseepage of such a polymerizing adhesive into the parent artery exists,if it is not completely blocked with consequent occlusion of the artery.

Still further, the prior art has utilized an air gun to inject hog hairthrough the aneurysm wall to induce internal thrombosis. The success ofthis procedure involves exposing the aneurysm sufficiently to allow airgun injection and has not been convincingly shown as successful forthrombic formations.

Ferromagnetic thrombosis in the prior art in extra-intravasculartreatments comprises the stereotactic placement of a magnetic probeagainst the sac of the aneurysm followed by injection into the aneurysmby an injecting needle of iron microspheres. Aggregation of themicrospheres through the extravascular magnet is followed byinterneuysmatic thrombus. This treatment has not been entirelysuccessful because of the risk of fragmentation of the metallic thrombuswhen the extravascular magnet is removed. Suspension of the iron powderin methyl methylmethacrylate has been used to prevent fragmentation. Thetreatment has not been favored, because of the need to puncture theaneurysm, the risk of occlusion of the parent artery, the use of unusualand expensive equipment, the need for a craniectomy and generalanesthesia, and the necessity to penetrate cerebral tissue to reach theaneurysm.

Endovascular coagulation of blood is also well known in the art and adevice using laser optically generated heat is shown by O'Reilly,"Optical Fiber with Attachable Metallic Tip for Intravascular LaserCoagulation of Arteries. Veins, Aneurysms, Vascular Malformation andArteriovenous Fistulas", U.S. Pat. No. 4,735,201 (1988). See also,O'Reilly et al., "Laser Induced Thermal Occlusion of Berry Aneurysms:Initial Experimental Results", Radiology, Vol. 171, No. 2, pages 471-74(1989). O'Reilly places a tip into an aneurysm by means of anendovascular microcatheter. The tip is adhesively bonded to a opticfiber disposed through the microcatheter. Optical energy is transmittedalong the optic fiber from a remote laser at the proximal end of themicrocatheter. The optical energy heats the tip to cauterize the tissuesurrounding the neck of the aneurysm or other vascular opening to beoccluded. The catheter is provided with a balloon located on or adjacentto its distal end to cut off blood flow to the site to be cauterized andoccluded. Normally, the blood flow would carry away the heat at thecatheter tip, thereby preventing cauterization. The heat in the tip alsoserves to melt the adhesive used to secure the tip to the distal end ofthe optical fiber. If all goes well the tip can be separated from theoptical fiber and left in place in the neck of the aneurysm, providedthat the cauterization is complete at the same time as the hot meltadhesive melts.

A thrombus is not formed from the heated tip. Instead, blood tissuesurrounding the tip is coagulated. Coagulation is a denaturation ofprotein to form a connective-like tissue similar to that which occurswhen the albumen of an egg is heated and coagulates from a clear runningliquid to an opaque white solid. The tissue characteristics andcomposition of the coagulated tissue is therefore substantially distinctfrom the thrombosis which is formed by the thrombotic aggregation ofwhite and red blood cells, platelets and fibrinogen. The coagulativetissue is substantially softer than a thrombic mass and can thereforemore easily be dislodged.

O'Reilly's device depends at least in part upon the successfulcauterization timed to occur no later than the detachment of the heattip from the optic fiber. The heated tip must also be proportionallysized to the neck of the aneurysm in order to effectively coagulate thetissue surrounding it to form a blockage at the neck. It is believedthat the tissue in the interior of the aneurysm remains substantiallyuncoagulated. In addition, the hot melt adhesive attaching the tip tothe optic fiber melts and is dispersed into the adjacent blood tissuewhere it resolidifies to form free particles within the intracranialblood stream with much the same disadvantages which result fromfragmentation of a ferromagnetic electro thrombosis.

Therefore, what is needed is an apparatus and methodology which avoidseach of the shortcomings and limitations of the prior art discussedabove.

BRIEF SUMMARY OF THE INVENTION

The invention is a method for forming an occlusion within a vascularcavity having blood disposed therein comprising the steps ofendovascularly disposing a wire and/or tip near an endovascular openinginto the vascular cavity. The wire may include a distinguishablestructure at its distal end, which is termed a tip, in which case theremaining portion of the wire may be termed a guidewire. The term "wire"should be understood to collectively include both guidewires and tipsand simply wires without distinct tip structures. However, the tip mayalso simply be the extension of the wire itself without substantialdistinction in its nature. A distal tip of the wire is disposed into thevascular cavity to pack the cavity to mechanically form the occlusionwithin the vascular cavity about the distal tip. The distal tip isdetached from the guidewire (or wire) to leave the distal tip within thevascular cavity. As a result, the vascular cavity is occluded by thedistal tip, and by any thrombus formed by use of the tip.

In one embodiment, the step of detaching the distal tip from theguidewire (or wire) comprises the step of mechanically detaching thedistal tip from the guidewire (or wire).

In another embodiment, the guidewire and tip (or wire) are used within amicrocatheter and in the step of detaching the distal tip from theguidewire (or wire), the guidewire and tip (or wire) are longitudinallydisplaced within the microcatheter. The microcatheter has radio-opaqueproximal and tip markers. The guidewire and tip (or wire) havecollectively a single radio-opaque marker. The displacement of theguidewire and tip (or wire) moves the single radio-opaque marker to theproximity of the proximal marker on the microcatheter. At this point thetip will be fully deployed in the vascular cavity and tip separation mayproceed. It is not necessary then in this embodiment to be able to seeactual deployment of the tip before separation. The tip marker allowsand enhances direct observation of the correct placement of the cathetertip into the opening of the vascular cavity.

In one embodiment the step of disposing the tip (or wire) into thevascular cavity to pack the cavity comprises the step of disposing a tip(or wire) having a plurality of filaments extending therefrom to packthe cavity.

In another embodiment the step of disposing the tip (or wire) into thevascular cavity to pack the cavity comprises the step of disposing along flexible tip (or wire) folded upon itself a multiple number oftimes to pack the cavity.

The invention can also be characterized as a method for forming anocclusion within a vascular cavity having blood disposed thereincomprising the steps of endovascularly disposing a wire within amicrocatheter near an endovascular opening into the vascular cavity. Themicrocatheter has a distal tip electrode. The distal tip of the wire isdisposed into the vascular cavity to pack the cavity to form theocclusion within the vascular cavity about the distal tip of the wire byapplying a current between the distal tip electrode and the distal endof the wire packed into the cavity. The distal tip of the wire isdetached from the wire to leave the distal tip of the wire within thevascular cavity. As a result, the vascular cavity is occluded by thedistal tip, and by any thrombus formed by use of the tip.

The invention is also a wire for use in formation of an occlusion withina vascular cavity used in combination with a microcatheter comprising acore wire, and a detachable elongate tip portion extending the core wirefor a predetermined lineal extent. The tip portion is adapted to bepacked into the vascular cavity to form the occlusion in the vascularcavity and coupled to the distal portion of the core wire. As a result,endovascular occlusion of the vascular cavity can be performed.

In one embodiment, the elongate tip portion is a long and substantiallypliable segment adapted to be multiply folded upon itself tosubstantially pack said vascular cavity.

In another embodiment, the elongate tip portion is a segment adapted tobe disposed in said vascular cavity and having a plurality of filamentsextending therefrom to substantially pack said vascular cavity whendisposed therein.

In still another embodiment, the microcatheter has a pair of radioopaquemarkers disposed thereon and the core wire has a radioopaque markerdisposed thereon. The marker on the core wire is positioned in theproximity of one of the pair of markers on the microcatheter when thecore wire is fully deployed. The other marker on the core wire marks theposition of the catheter tip.

The invention is still further characterized as a microcatheter systemfor use in formation of an occlusion within a vascular cavity comprisinga microcatheter having a distal end adapted for disposition in theproximity of the vascular cavity. The distal end has an electrodedisposed thereon. A conductive guidewire is disposed in themicrocatheter and longitudinally displaceable therein. The guidewirecomprises a core wire, and an elongate tip portion extending the corewire for a predetermined lineal extent. The tip portion is adapted to bepacked into the vascular cavity to form the occlusion in the vascularcavity. The tip portion is coupled to the distal portion of the corewire. The occlusion is formed by means of applying a current between thetip portion and the electrode on the microcatheter when the tip portionis disposed into the vascular cavity. As a result, endovascularocclusion of the vascular cavity can be performed.

More generally speaking, the invention is a method for forming anocclusion within a vascular cavity having blood disposed thereincomprising the steps of disposing a body into the cavity tosubstantially impede movement of blood in the cavity. The body isemployed in the cavity to form the occlusion within the vascular cavity.As a result, the vascular cavity is occluded by the body.

The step of disposing the body in the vascular cavity comprises the stepof packing the body to substantially obstruct the cavity.

In one embodiment the step of packing the cavity with the body comprisesthe step of obstructing the cavity with a detachable elongate wire tipmultiply folded upon itself in the cavity.

The step of disposing the body into the vascular cavity comprisesdisposing in the vascular cavity means for slowing blood movement in thecavity to initiate formation of the occlusion in the cavity.

In another embodiment the step of packing the cavity with the bodycomprises the step of obstructing the cavity with a body having acompound filamentary shape.

The step of employing the body in the vascular cavity to form theocclusion comprises the step of applying an electrical current to thebody or mechanically forming the occlusion in the body or bothsimultaneously.

The invention is also wire for use in formation of an occlusion within avascular cavity used in combination with a microcatheter. The inventioncomprises a core wire and a detachable elongate tip portion extendingthe core wire for a predetermined lineal extent. The core wire isadapted to being packed into the vascular cavity to form the occlusionin the vascular cavity and is coupled to the distal portion of the corewire. The tip portion includes a first segment for disposition into thecavity and a second segment for coupling the first portion to the corewire. The second segment is adapted to be electrolysized uponapplication of current. An insulating coating is disposed on the firstsegment. The second segment is left exposed to permit selectiveelectrolysis thereof. As a result, endovascular occlusion of thevascular cavity can be performed.

The invention can better be visualized by now turning to the followingdrawings wherein like elements are referenced by like numerals.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged partially cross-sectioned side view of a firstembodiment of the distal end of the guidewire and tip of the invention.

FIG. 2 is an enlarged longitudinal cross section of a second embodimentof the guidewire and tip of the invention.

FIG. 3 is an enlarged side view of a third embodiment of the inventionwith a microcatheter portion cut away in a longitudinal cross-sectionalview.

FIG. 4 is a simplified depiction of the wire of FIG. 3 shown disposedwithin a simple cranial aneurysm.

FIG. 5 is a depiction of the wire of FIG. 4 shown after electrolyticdetachment of the tip.

FIG. 6 is a plan view of another embodiment of the guidewire and tipportion wherein the type is provided with a plurality of polyesterfilamentary hairs.

FIGS. 7 and 8 are a diagrammatic depictions of the use of the inventionwherein position markers have been provided on the catheter and wire toassist in proper fluoroscopic manipulation.

FIG. 9 is a simplified cross-sectional view of the catheter and wireshowing a ground electrode disposed on the distal tip of the catheter.

The invention and its various embodiments are best understood by nowturning to the following detailed description.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An artery, vein, aneurysm, vascular malformation or arterial fistula isoccluded through endovascular occlusion by the endovascular insertion ofa platinum tip into the vascular cavity. The vascular cavity is packedwith the tip to obstruct blood flow or access of blood in the cavitysuch that the blood clots in the cavity and an occlusion if formed. Thetip may be elongate and flexible so that it packs the cavity by beingfolded upon itself a multiple number of times, or may pack the cavity byvirtue of a filamentary or fuzz structure of the tip. The tip is thenseparated from the wire mechanically or by electrolytic separation ofthe tip from the wire. The wire and the microcatheter are thereafterremoved leaving the tip embedded in the thrombus formed within thevascular cavity. Movement of wire in the microcatheter is more easilytracked by providing a radioopaque proximal marker on the microcatheterand a corresponding indicator marker on the wire. Electrothrombosis isfacilitate by placing the ground electrode on the distal end of themicrocatheter and flowing current between the microcatheter electrodeand the tip.

When the tip is separated from the wire by electrolytic separation ofthe tip from the wire, a portion of the wire connected between the tipand the body of the wire is comprised of stainless steel and exposed tothe bloodstream so that upon continued application of a positive currentto the exposed portion, the exposed portion is corroded away at least atone location and the tip is separated from the body of the wire.

FIG. 1 is an enlarged side view of a first embodiment of the distal endof the wire and tip shown in partial cross-sectional view. Aconventional Teflon laminated or similarly insulated stainless steelwire 10 is disposed within a protective microcatheter (not shown).Stainless steel wire 10 is approximately 0.010-0.020 inch (0.254-0.508mm) in diameter. In the illustrated embodiment, wire 10 is tapered atits distal end to form a conical section 12 which joins a section 14 ofreduced diameter which extends longitudinally along a length 16 of wire10. Section 16 then narrows gradually down to a thin threadlike portion18 beginning at a first bonding location 20 and ending at a secondbonding location 22.

The stainless steel wire 10, comprised of that portion disposed withinthe microcatheter body, tapered section 12, reduced diameter section 16and threadlike section 18, is collectively referred to as a core wirewhich typically is 50-300 cm. in length.

In the illustrated embodiment the portion of the core wire extendingfrom tapered section 12 to second bonding location 22 is collectivelyreferred to as the grinding length and may typically be between 20 and50 cm. in length.

Reduced diameter portion 14 and at least part of sections 12 and firstbonding location 20 may be covered with an insulating Teflon laminate 24which encapsulates the underlying portion of wire 10 to prevent contactwith the blood.

A stainless steel coil 26 is soldered to the proximate end of threadlikeportion 18 of wire 10 at first bonding location 20. Stainless steel coil26 is typically 3 to 10 cm. in length and like wire 10 has a diametertypically between 0.010 to 0.020 inch (0.254-0.508 mm).

The distal end of stainless steel coil 26 is soldered to the distal endof threadlike portion 18 of wire 10 and to the proximal end of aplatinum secondary coil 28 at second bonding location 22. Secondary coil28 itself forms a spiral or helix typically between 2 to 10 mm. indiameter. The helical envelope formed by secondary coil 28 may becylindrical or conical. Like wire 10 and stainless steel coil 26,secondary coil 28 is between approximately 0.010 and 0.020 inch(0.254-0.508 mm) in diameter. The diameter of the wire itself formingstainless steel coil 26 and coil 28 is approximately between 0.001-0.005inch.

The distal end of secondary coil 28 is provided with a platinum solderedtip 30 to form a rounded and smooth termination to avoid puncturing theaneurysm or tearing tissue.

Although prebiased to form a cylindrical or conical envelope, secondarycoil 28 is extremely soft and its overall shape is easily deformed. Wheninserted within the microcatheter (not shown), secondary coil 28 iseasily straightened to lie axially within the microcatheter. Oncedisposed out of the tip of the microcatheter, secondary coil 28 formsthe shape shown in FIG. 1 and may similarly be loosely deformed to theinterior shape of the aneurysm.

As will be described below in greater detail in connection with thethird embodiment of FIG. 3, after placement of secondary coil 28 withinthe interior of the aneurysm, a direct current is applied to wire 10from a voltage source exterior to the body. The positive charge onsecondary coil 28 within the cavity of the aneurysm causes a thrombus toform within the aneurysm by electrothrombosis. Detachment of the tipoccurs either: (1) by continued application of current for apredetermined time when the portion 18 is exposed to blood; or (2) bymovement of the wire to expose portion 18 to blood followed by continuedcurrent application for a predetermined time. Ultimately, boththreadlike portion and stainless steel coil 26 will be completelydisintegrated at least at one point, thereby allowing wire 10 to bewithdrawn from the vascular space while leaving secondary coil 28embedded within the thrombus formed within the aneurysm.

FIG. 2 illustrates in enlarged partially cross-sectional view a secondembodiment of the invention. Stainless steel core 32 terminates in aconical distal portion 34. Stainless steel coil 36, shown incross-sectional view, is soldered to distal portion 34 of wire 32 atbonding location 38. The opposing end of the stainless steel coil 36 isprovided with a soldered, rounded platinum tip 40. In the illustratedembodiment, stainless steel core wire 32 is approximately 0.010 inch indiameter with the length of stainless steel coil 36 being approximately8 cm. with the longitudinal length of platinum tip 40 being between 3and 10 mm. The total length of wire 32 from tip 40 to the proximate endis approximately 150 cm.

The embodiment of FIG. 2 is utilized in exactly the same manner asdescribed above in connection with FIG. 1 to form a thrombic mass withinan aneurysm or other vascular cavity. The embodiment of FIG. 2 isdistinguished from that shown in FIG. 1 by the absence of the extensionof stainless core 32 through coil 36 to tip 40. In the case of theembodiment of FIG. 2 no inner core or reinforcement is provided withinstainless steel coil 36. Threadlike portion 18 is provided in theembodiment of FIG. 1 to allow increased tensile strength of the wire.However, a degree of flexibility of the wire is sacrificed by theinclusion even of threadlike tip 18, so that the embodiment of FIG. 2provides a more flexible tip, at least for that portion of themicro-guidewire constituting the stainless steel coil 36.

It is expressly understood that the helical secondary coil tip of theembodiment of FIG. 1 could similarly be attached to stainless steel coil36 of the embodiment of FIG. 2 without departing from the spirit andscope of the invention.

Thinned and threadlike portion guidewires disposed concentrically withincoiled portions are well known and are shown in Antoshkiw, "DisposableGuidewire", U.S. Pat. No. 3,789,841 (1974); Sepetka et al., "GuidewireDevice", U.S. Pat. No. 4,832,047 (1989); Engelson, "Catheter Guidewire",U.S. Pat. No. 4,884,579 (1989); Samson et al., "Guidewire forCatheters", U.S. Pat. No. 4,538,622 (1985); and Samson et al., "CatheterGuidewire with Short Spring Tip and Method of Using the Same", U.S. Pat.No. 4,554,929 (1985).

Turn now to the third embodiment of the invention as shown in FIG. 3.FIG. 3 shows an enlarged side view of a wire, generally denoted byreference numeral 42, disposed within a microcatheter 44 shown incross-sectional view. Like the embodiment of FIG. 1, a stainless steelcoil 46 is soldered to a conical portion 48 of wire 22 at a firstbonding location 50. A thin threadlike extension 52 is thenlongitudinally disposed within stainless steel coil 46 to a secondbonding location 54 where stainless steel wire 46 and threadlike portion52 are soldered to a soft platinum coil 56. Platinum coil 56 is notprebiased, nor does it contain any internal reinforcement, but is a freeand open coil similar in that respect to stainless steel coil 36 of theembodiment of FIG. 2.

However, platinum coil 56 is particularly distinguished by its length ofapproximately 1 to 50 cm. and by its flexibility. The platinum orplatinum alloy used is particularly pliable and the diameter of the wireused to form platinum coil 56 is approximately 0.001-0.005 inch indiameter. The distal end of platinum coil 56 is provided with a smoothand rounded platinum tip 58 similar in that respect to tips 30 and 40 ofFIGS. 1 and 2, respectively.

When coil 56 is disposed within microcatheter 44, it lies along thelongitudinal lumen 60 defined by microcatheter 44. The distal end 62 ofmicrocatheter 60 is then placed into the neck of the aneurysm and thewire 42 is advanced, thereby feeding tip 58 in platinum coil 56 intoaneurysm 64 until bonding location 50 resides in the neck of theaneurysm as best depicted in the diagrammatic cross-sectional view ofFIG. 4.

FIG. 4 illustrates the insertion of the embodiment of FIG. 3 within avessel 66 with distal tip of microcatheter 44 positioned near neck 68 ofaneurysm 64. Coil 56 is fed into aneurysm 64 until at least a portion ofstainless steel coil 46 is exposed beyond the distal tip 62 ofmicrocatheter 44. A positive electric current of approximately 0.01 to 2milliamps at 0.1-6 volts is applied to wire 42 to form the thrombus.Typically a thrombus will form within three to five minutes. Thenegative pole 72 of voltage source 70 is typically placed over and incontact with the skin.

After the thrombus has been formed and the aneurysm completely occluded,tip 58 and coil 56 are detached from wire 42 by electrolyticdisintegration of at least one portion of stainless steel coil 46. Inthe illustrated embodiment this is accomplished by continued applicationof current until the total time of current application is almostapproximately four minutes.

At least one portion of stainless steel coil 46 will be completelydissolved through by electrolytic action within 3 to 10 minutes, usuallyabout 4 minutes. After separation by electrolytic disintegration, wire42, microcatheter 44 and the remaining portion of coil 46 still attachedto wire 42 are removed from vessel 66, leaving aneurysm 64 completelyoccluded as diagrammatically depicted in FIG. 5 by thrombus 74. It willbe appreciated that the time of disintegration may be varied by alteringthe dimensions of the portions of the wire and/or the current.

The process is practiced under fluoroscopic control with localanesthesia at the groin. A transfemoral microcatheter is utilized totreat the cerebral aneurysm. The platinum is not affected byelectrolysis and the remaining portions of the microcatheter areinsulated either by a Teflon lamination directly on wire 42 and/or bymicrocatheter 44. Only the exposed portion of the wire 46 is affected bythe electrolysis.

It has further been discovered that thrombus 74 continues to form evenafter detachment from wire 42. It is believed that a positive charge isretained on or near coil 56 which therefore continues to attractplatelets, white blood cells, red blood cells and fibrinogen withinaneurysm 64.

Although the foregoing embodiment has been described as forming anocclusion within a blood-filled vascular cavity by means ofelectrothrombosis, the above disclosure must be read to expresslyinclude formation of the occlusion by mechanical mechanisms withoutresort to the application of electrical current. A mechanical mechanismwhich can be safely disposed into the vascular cavity to impede, slow orotherwise initiate clotting of the blood or formation of the occlusionis within the scope of the invention. The insertion within the vascularcavity and maintenance therein of an object with an appropriateblood-clotting characteristics can and does in many cases cause theformation of an occlusion by itself. Depicted in FIG. 6 is an embodimentof the invention wherein such mechanical thrombosis can be achieved.Wire 10 has a tapering end portion 14 covered with a Teflon laminate 24similar to that described in connection with the embodiment of FIG. 1.Wire 10 is attached by means of a mechanical coupling 100 to a platinumcoil 102 which has a plurality of filaments or fine hairs 104 extendingtherefrom. In the illustrated embodiment, hairs 104 have a length as maybe determined from the size of the vascular cavity in which coil 102 isto be used. For example, in a small vessel hair lengths of up to 1 mmare contemplated. An example of polyester filaments or hairs attached toa coil which was not used in electrothrombosis may be seen in thecopending application entitled Vasoocclusion Coil with Attached FiberousElements, filed Oct. 2, 1991, Ser. No. 07/771,013.

Coil 102 has sufficient length and flexibility that it can be insertedor coiled loosely into the vascular cavity. The length of coil 102 neednot be so long that the coil itself is capable of being multiply foldedon itself and fill or substantially fill the vascular cavity. Hairs 104extending from coil 102 serve to substantially pack, fill or at leastimpede blood flow or access in the vascular cavity. Hairs 104, which aregenerally inclined backwardly away from extreme tip 106 when delivered,are thus easily able to slide forward with little friction throughrestrictions in the vessels and aneurysm. Additionally, hairs 104 do nothave sufficient length, strength or sharpness to provide any substantialrisk or potential for a puncture of the thin vascular wall. Theplurality of hairs 104, when coiled within the vascular cavity, providean extremely large surface for attachment of blood constituents toencourage and enhance the formation of a mechanical occlusion within thevascular opening.

In the preferred embodiment, coil 102 is mechanically coupled to thintapered portion 104 of wire 10 by means of a small drop of polyester100. Polyester may be substituted for the gold solder of the previouslydescribed embodiments in order to reduce concern or risk of toxicreactions in the body.

Tip portion 104 may also be mechanically separated from wire 10 by meansother than electrolysis. One method is make the connection between tip104 and wire 10 by means of a spring loaded mechanical clasp (notshown). The clasps are retained on tip 104 as long as the clasps remaininside of the catheter, but spring open and release tip 104 whenextended from the catheter. The catheter and clasps may then be removedfrom the insertion site. This type of mechanical connection is describedin the copending application entitled, "Detachable Pusher-VasoocclusiveCoil Assembly with Interlocking Coupling", filed Dec. 12, 1991 with Ser.No. 07/806,979 which is Incorporated herein by reference and assigned toTarget Therapeutics Inc. An alternative nonresilient mechanical ball andclasp capturing mechanism is described in the copending applicationentitled "Detachable Pusher-Vasoocclusive Coil Assembly withInterlocking Bail and Keyway Coupling", filed Dec. 12, 1991 with Ser.No. 07/806,912 which is also incorporated herein by reference andassigned to Target Therapeutics Inc.

In another embodiment wire 10 and tip portion 104 screw into each otherand can be unscrewed from each other by rotation of the catheter or wirewith respect to tip 104. An extendable sheath (not shown) in themicrocatheter is advanced to seize tip 104 to prevent its rotation withwire 10 during the unscrewing process. This type of mechanicalconnection is described in the copending application entitled"Detachable Pusher-Vasoocclusive Coil Assembly with Threaded Coupling",filed Dec. 12, 1991 with Ser. No. 07/806,898 which is incorporatedherein by reference and assigned to Target Therapeutics Inc.

In any case the specific means disclosed here of mechanically detachingtip 104 from wire 10 forms no part of the present invention apart fromits combination as a whole with other elements of the invention.Specific disclosure of the mechanical means of detachment have been setforth only for the purposes of providing an enabling disclosure of thebest mode presently known for practicing the claimed invention.

Even where the occlusion is not formed by electrothrombosis, separationof tip 104 may be effected by electrolysis. In such situations, theelectrolysing current may be concentrated on the sacrificial stainlesssteel portion of tip 104 by disposition of an insulative coating on theremaining platinum portion. For example, tip 104 may be provided with apolyethylene coating save at least a portion of the stainless steellength. This has the effect of decreasing the time required toelectrolytically sufficiently disintegrate the steel portion to allowdetachment of the platinum tip, which is an advantageous feature inthose cases where a large aneurysm must be treated and a multiple numberof coils must be deployed within the aneurysm.

Notwithstanding the fact that wire 10 and platinum coil 102 in theembodiment FIG. 6 or wire 10 and platinum coil 28, 36 and 56 in theembodiments of FIGS. 1-5 are radiopaque, there is still some difficultywhen manipulating the device under fluoroscopy to be able to determinethe exact position or movement of the probe relative to the aneurysm.This is particularly true when a large number of coils are deployed andone coil then radiographically hides another. FIG. 7 illustrates animprovement of, for example, the embodiment of FIGS. 4 and 5.Microcatheter 144 is positioned so that its distal end 162 within vessel66 is positioned at the opening aneurysm 64. Microcatheter 144 isprovided with radiopaque marker 108 at distal tip 162, a tip marker.Moving toward the proximal end of microcatheter 144 is a secondradiopaque marker 110, a proximal marker. Radiopaque markers 108 and 110are, for example, in the form of radiopaque rings made of platinumapproximately 1-3 mm in longitudinal length along the axis ofmicrocatheter 144. Rings 110 and 108 are typically separated by about 3cm on microcatheter 144. Similarly, wire 10 has a radiopaque marker 112defined on it such that marker 112 on wire 10 is approximately withaligned with marker 110 on microcatheter 14 when coil 56 is fullydeployed into aneurysm 64. Typically, full deployment will place thesolder or connection point 54 of the order of 2-3 mm past opening 68 ofaneurysm 64. Distal marker 108 on microcatheter 144 is used tofacilitate the location of the microcatheter tip, which can often beobscured by the coils which have been previously deployed. The coils area varying lengths depending on the application or size of the aneurysmor vascular cavity being treated. Coil lengths of 4-40 cm are common.Therefore, even though the thinness of coil 56 may make it difficult tosee under standard fluoroscopy and even though the fineness of wire 10may similarly be obscured or partly obscured, radiopaque markers 108,110 and 112 are clearly visible. Manipulation of wire 10 to proximalmarker 110 can then easily be observed under conventional fluoroscopyeven when there are some loss of resolution or fluoroscopic visualobstruction of the coil.

Further, in the previous embodiments, such as that shown in FIGS. 4 and5, when electrothrombosis is used to form the occlusion within vascularaneurysm 64, coil 56 is used as the electrical anode while the cathodeis a large skin electrode 72 typically conductively applied to the groinor scalp. FIG. 9 illustrates an alternative embodiment whereinmicrocatheter 144 is supplied with an end electrode 114 coupled to anelectrical conductor 116 disposed along the length of microcatheter 144.Wire 116 is ultimately led back to voltage source 70 so that ringelectrode 114 is used as the cathode during electrothrombosis instead ofan exterior skin electrode 72. With the embodiment of FIG. 9, theelectrical currents and electrical current paths which are set up duringthe electrothrombosis formation are local to the site of applicationwhich allows even smaller currents and voltages to be used to initiateelectrothrombosis than in the situation when an exterior skin electrodemust be utilized. The electrothrombosic current distributions are alsobetter controlled and localized to the site of the thrombus formation.The possibility of stray thrombus formations occurring at unwanted sitesor uncontrolled and possibly unwanted electrical current patterns beingestablished elsewhere in the brain or body is therefore largely avoided.

Many alterations and modifications may be made by those having ordinaryskill in the art without departing from the spirit and scope of theinvention. Therefore, it must be understood that the shape of the tip ordistal platinum coil used in combination with the wire according to theinvention may be provided with a variety of shapes and envelopes. Inaddition thereto, the composition of the micro-guidewire tip may be madeof elements other than platinum including stainless steel beryllium,copper and various alloys of the same with or without platinum. Stillfurther, the diameter of the wire, various of the wire described aboveand the stainless steel coil immediately proximal to the detachable tipmay be provided with differing diameters or cross sections to vary thetimes and current magnitudes necessary in order to effectuateelectrolytic detachment from the tip. Still further, the invention mayinclude conventional electronics connected to the proximal end of thewire for determining the exact instant of detachment of the distal tipfrom the wire.

Therefore, the illustrated embodiment has been set forth only for thepurposes of clarity and example and should not be taken as limiting theinvention as defined by the following claims, which include allequivalent means whether now known or later devised.

We claim:
 1. An apparatus for use in electrothrombosis in combinationwith a microcatheter the apparatus comprising:a core wire having a mainbody with a distal portion and a detachable coil coupled to said mainbody via said distal portion and comprised of material not susceptibleto electrolytic disintegration, said detachable coil containing nointernal reinforcement and being for insertion within a body cavity;wherein said distal portion is susceptible to electrolyticdisintegration so that on the application of current to the apparatuswhen said detachable coil is disposed in the cavity, electrothrombosiscan be performed and at least one portion of said distal portionelectrolytically disintegrated to detach said detachable coil from saidmain body.
 2. The apparatus of claim 1 wherein said distal portion isexposed stainless steel comprising a stainless steel coil connected atits proximal end to said core wire and connected at its distal end tosaid detachable coil, and wherein said distal portion further comprisesa threadlike extension of the main body of the core wire extendingconcentrically within said stainless steel coil and connected at itsdistal end to the connection of the distal end of the stainless steelcoil and the detachable coil both said threadlike extension and saidstainless steel coil needing to be electrolytically disintegrated atleast at one point in order to detach the detachable coil from the mainbody.
 3. The apparatus of claim 1 wherein said distal portion is exposedstainless steel comprising a stainless steel coil connected at itsproximal end to said core wire and connected at its distal end to saiddetachable coil, and wherein said stainless steel coil defines aninterior space, said interior space being free and unreinforced.
 4. Theapparatus of claim 1, wherein the detachable coil is a long and pliablesegment.
 5. The apparatus of claim 4 wherein said detachable coil has alength sufficient to substantially fill the cavity when disposedtherein.
 6. The apparatus of claim 1 wherein the detachable coil iscomprised of a metal not susceptible to electrolytic disintegration. 7.The apparatus of claim 1 wherein the detachable coil is prebiased toform a helix or spiral when advanced from a microcatheter into thecavity.
 8. The apparatus of claim 7 wherein the detachable coil isprebiased to have a conical envelope.
 9. The apparatus of claim 7wherein the detachable coil is prebiased to have a cylindrical envelope.10. The apparatus of claim 7 wherein although prebiased the detachablecoil is extremely soft and its overall shape is easily deformed suchthat, once advanced from a microcatheter into the cavity, it willloosely deform to the interior shape of the cavity.
 11. The apparatus ofclaim 1 wherein the detachable coil is unbiased.
 12. The apparatus ofclaim 1 wherein the main body of the core wire is covered withinsulation to prevent the underlying portion of the apparatus fromcoming into contact with any fluid.